Tungsten base alloy



United States Patent Office 3,030,229 Patented Mar. 5, 1963 3,080,229 TUNGSTEN BASE ALLQY Richard W. Heckcl, Wilmington, Del, msignor to E. I. du Pont de Nemours and Compan Wihnington, Dei,

a corporation of Delaware No Drawing. Filed Oct. 11, 1960, Ser. No. 61,848

15 Claims. (Cl. 75-476) This invention relates to high-ternperature alloys which have tungsten metal as a base, and which contain as essential ingredients the metals colurnbium and titanium.

It has been found that the oxidation resistance of tungsten can be improved and other valuable properties of the metal, such as the high-temperature strength and fabricability, retained at the original level or improved, by the alloying of tungsten with the metals columbium and titanium. More specifically, it has been found that in this ternary alloy system, two compositional areas exhibit greatly improved oxidation resistance over previously known alloys.

The first compositional area includes alloys comprising about 75-95% tungsten, about 4.8-24.8% columbium, and about 0.212.5% titanium. A preferred compositional range within this first area comprises about 7'794.6% tungsten, about %18% colum-bium, and about 04-80% titanium.

The second compositional area includes alloys comprising about 42-65% tungsten, about 17.542.5% columbium, and about 7.5-27.5 titanium. A preferred compositional range. within this second area comprises about 4360% tungsten, about 2041.5% columbium, and about 9-23% titanium.

1 ie alloys of this invention are preferably made from commercial metal powders of the highest purity available. Because of the extremely high melting point of tungsten and the high vapor pressure of titanium and columbium at the temperatures under which the alloys of this invention are prepared, it is sometimes di-tlicult to prepare these alloys without loss of some amount of one or both of the alloying elements. Therefore, the compositions defined herein are analyzed compositions.

In the preparation of the tungsten-base alloys of this invention, several different methods can be used. The alloys can be prepared by the method of arc melting of the metal powders. In this type of procedure, the metal powders are blended and thoroughly mixed in the proper proportions to yield the desired nominal composition. If desired, the powder mixture can be compacted into small billets before melting. Because of differences in melting points. and in, vapor pressures of the alloying elements at high temperatures, loss by volatilization during melting may thus. be minimized; also, some losses may be accounted for by scattering of the powder by the arc. Compaction minimizes such losses. However, the powder mixture can be melted directly without compaction. The alloys are usually melted four times, the castings being turned over between meltings in order to insure homogeneity of composition in the melt. After melting, most of the alloys were homogenized in vacuum at temperatures from 1750 C. to 2200 C. for periods of about /2 hour to about 4 hours.

For clearer understanding of the invention, the following specific examples are given. These examples are intended to be merely illustrative of the invention and not in limitation thereof. Unless otherwise specified, all parts are by weight.

EXAMPLE I An alloy of tungsten, columbium, and titanium was prepared as follows:

A mixture of powdered metals comprising 90 parts tungsten, 5 parts columbium, and 5 parts titanium was thoroughly blended and formed into a compact under a pressure of 50 t.-s.i. This compact was then are melted under vacuum and coo-led. The casting was then turned over and remelted, the melting process being carried out four times to insure homogeneity in the sample. By analysis, the composition of the alloy so prepared was found to contain: 94.5% W, 5.1% Nb, 0.4% Ti.

The alloy sample thus prepared was carefully ground so that two faces of the alloy sample were parallel and flat. Preparations were then made for testing the oxidation resistance of the alloy. The thickness and surface area of the sample were measured. It was then weighed and heated to 1200" C. while a flow of dry air at 1000 cc./min. was directed over the sample. These conditions were maintained for 5 hours. After furnace cool ing, the sample was reweighed and the gain in weight per unit of surface area (mg/cm. area) was determined. The sample was then mounted for metallographic examination and surface recession measurements were taken. These results are reported in Table I below, along with the results of other alloys prepared and tested.

EXAMPLE II An alloy of tungsten, columbium, and titanium was prepared as follows: parts tungsten, 1'0- par-ts columbium, and 5 parts titanium, all in powder form, were blended and melted. In this example, the powder mix was not compacted prior to melting. The alloy was allowed to cool and was remelted four times, with the casting being turned over between melts. The analyzed composition of the alloy was: 11.1% Nb, 2.5% Ti, balance W. Following the melting, the alloy was homogenized by heating at 1750 C. for 4 hours. The alloy sample thus prepared was tested for oxidation resistance by directing a flow of dry air at 1000 cc./min. over the sample at 1200 C. for 5 hours. After furnace cooling, the sample wasreweighed and the gain in weight per unit of surface area (mg/cm?) was determined. The sample was then mounted for metallographic examination and surface recession measurements were taken. The results of these tests are recorded in, Table 1 below.

Other alloys were prepared according to the procedures given in Examples I and H and the results of tests for oxidation resistance are. summarized below.

Table 1 Composition. (wt. percent) Surface Weight Alloy No. recession gain W Nb Ti (0111.) (mg/cm!) (Analyzed) 0 0 0.06 i h 290. 0 0 0.066 523. 5.1 0.4 0.023 109. 11.1 2.5 0.013 64. 10.8 2.9 0.012 84. 17.0 8.0 0.015 150. 17.8 4.3 0.013] 129. 21.7 9.8 unevenattack 183. 11.0 22.4 0.154 42 i. 28.3 5.0 completely completely oxidized. oxidized 32.0 9.4 25.7 16,8 21.0 19.9 8.0 22.1 30.8 10.0 41.1 14.7 31.6 19.8

1 Tested in the as cast condition. 2 Homogenized at 1750 O. for 4 hours.

Tests on unalloyed tungsten and a tungsten-columbium 9 binary (alloy No. 16) and alloys 6, 7, 8, and 12 are included in the above table to show that alloy compositions outside of this invention lack oxidation resistance and, in fact, in some cases show even less resistance to oxidation than does pure tungsten.

It is a generally accepted metallurgical fact that the retention of hardness at elevated temperatures is an indication of high temperature strength of metals and alloys. Two alloys were prepared according to the procedure given in Example I. These were tested, along with a sample of pure tungsten, for hot hardness at temperatures from room temperature to 1300 C. Results are shown in Table 11, following:

Table I1 DIAMOND PYRAMID HARDNESS OF TUNGSTEN AND TWO TUNGSTEN-BASE ALLOYS FROLI ROOM TElVIPERATURE UP TO 1300" C.

From these results it will be seen that these two alloys within the compositional areas covered by this invention retain a large degree of their hardness up to a temperature of 1200 C.

Other methods may be used to prepare the alloys of this invention. One method which has frequently been employed to effect alloying of tungsten with other elements has been to prepare compacts of metal powders and to elfect sintering of the compacted powder mix. A suggested method of compaction of metal powders is one in which the compaction is achieved by the carefully controlled detonation of an explosive charge. This explosive compaction of powder mixes has been very effectively employed in the preparation of dense compacts which are then sintered to effect alloying of the elements.

Another method which has been employed in the preparation of the tungsten-rich alloys of this invention is that of sealing uncompacted powder blends in stainless steel tubes. These tubes are heated to 1250 C., then rolled and forged. This process yields alloy slabs of almost full density. The stainless steel tubes in which the metal powders are heated may be evacuated to further minimize porosity of the compact.

The alloys of this invention will be found particularly adapted for use in applications where very high temperatures are encountered; and more especially where resistance to oxidation is required at elevated temperatures. Such appliactions include dies used in high-temperature extrusions and flame tips for gas burners. These alloys may also be fabricated into equipment for chemical and oil refining plants where resistance to oxidation at elevated temperatures is a requirement for materials of construction.

Since it is obvious that many changes and modifications can be made in the above-described details without departing from the nature and spirit of the invention, it is to be essentially tungsten in an amount not less than 75%.

2. An alloy resistant to oxidation at high temperatures consisting essentially of by weight about 77% to 94.6% tungsten, about 5% to 18% columbium, and about 0.4% to 8.0% titanium.

3. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 5.1% columbium, about 0.4% titanium, the balance being essentially tungsten.

4. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 11.1% columbium, about 2.5% titanium, the balance being essentially tungsten.

5. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 10.8% columbium, about 2.9% titanium, the balance being essentially tungsten.

6. A ternary alloy resistant to oxidation at high temperatures comprising by Weight about 17.8% columbium, about 4.3% titanium, the balance being essentially tungsten.

7. An alloy resistant to oxidation at high temperatures comprising by weight about 17.5% to 42.5% columbium, about 7.5% to 27.5% titanium, and the balance being essentially tungsten in an amount of about 42% to 65%.

8. An alloy resistant to oxidation at high temperatures consisting essentially of by weight about 43-60% tungsten, about 20%-41.5% columbium, and about 9%-23% titanium.

9. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 32% columbium, about 9.4% titanium, the balance being essentially tungsten.

10. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 25.7% columbium, about 16.8% titanium, the balance being essentially tungsten.

11. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 21.0% columbium, about 19.9% titanium, the balance being essentially tungsten.

12. A ternary alloy resistant to oxidation at high temperatures comprising by weight 30.8% columbium, about 10.0% titanium, the balance being essentially tungsten.

13. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 41.1% columbium, about 14.7% titanium, the balance being essentially tungsten.

14. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 31.6% columbium, about 19.8% titanium, the balance being essentially tungsten.

15. A ternary alloy resistant to oxidation at high temperatures comprising by weight about 17% columbium, about 8% titanium, the balance being essentially tungsten.

References Cited in the file of this patent Kiefler et al.: Tungsten Alloys of High Melting Point, vol. 1, February 1959, Journal of the Less-Common Metals, pages 19-33. 

2. AN ALLOY RESISTANT TO OXIDATION AT HIGH TEMPERATURES CONSISTING ESSENTIALLY OF BY WEIGHT ABOUT 77% TO
 94. 6% TUNGSTEN, ABOUT 5% TO 18% COLUMBIUM, AND ABOUT 0.4% TO
 8. 0% TITANIUM.
 8. AN ALLOY RESISTANT TO OXIDATION AT HIGH TEMPERATURES CONSISTING ESSENTIALLY OF BY WEIGHT ABOUT 43-60% TUNGSTEN, ABOUT 20%-41.5% COLUMBIUM, AND ABOUT 9%-23% TITANIUM. 